As is well known in the art, cylinder locks generally include a plug (also called tumbler) arranged for rotation in a lock cylinder housing. Plug pins are slidingly disposed in the plug and are arranged to move against driver pins, which are disposed in bores formed in the cylinder housing and are spring biased toward the axis of the plug rotation. Insertion of a properly cut key in a keyway provided in the plug moves the plug pins against the driver pins and aligns all the pins along a shear line defined by the plug outer circumference, thereby permitting rotation of the plug to cause operation of a latch or locking mechanism.
Cylinders locks are also known that are equipped with a movable element (e.g., pin) disposed in the key blade. An auxiliary locking pin is spring-loaded in the cylinder housing. Upon insertion of the key in the keyway, the movable element aligns with the auxiliary locking pin and interacts therewith to align with the shear line and permit rotation of the plug. Even if a would-be thief were to pick the key-cut combination of the key, he still would not defeat the lock without additionally aligning the movable element with the auxiliary locking pin. The latter action is very difficult without an authorized key, and thus the lock provides high security. Such locks are described, for example, in U.S. Pat. Nos. 5,520,035, 5,784,910 and 5,839,308 to Eizen et al., assigned to the assignee of the present application. These patents describe a key blank that includes a generally elongate shaft portion defining a key combination surface adapted to have formed thereon key cuts which define a key combination. The key blank includes a movable pin element retained within the elongate shaft portion. The movable pin element may be displaced in a single direction, outwardly from the key combination surface.